192 
ME. W. K. PARKER ON THE STRUCTURE AND 
Bibliographical references and comparisons ivith other Vertebrate types. 
Considering that the present paper is merely one of a series, and that its character is 
very special , there will be little need for reference to the invaluable works which have 
reference to the general structure and development of the Amphibia. 
The most important help, indeed, has been derived from works treating of other types , 
especially where the skeletal parts have been worked out. 
In my endeavour to make plain to others what to my own mind was for a long while 
a labyrinth of difficulties, I have had constant recourse to the works of Professor Huxley, 
especially his “ Croonian Lecture,” ‘ Elements,’ and ‘‘ Representatives of Malleus and 
Incus in other Vertebrata.” But such reference is only part of the matter; for we have 
been workers together in this research. 
Another most valued author, whose works have been always with me from my youth 
up, must be mentioned, viz. the late Professor Jon. Muller ; his Monograph on the 
4 Myxinoids ’ has been vital to this attempt to make plain the intricate morphology of 
the Batrachian skull. 
I shall make comparisons of the present subject with the structure of various Verte- 
brate types, and, first, may give 
A. A comparison of the Skull of the Common Frog ivith that of other “ Artur a C 
In the Bull-frog (Rana pipiens, L.), with a perfect general agreement, there are vari- 
ations in particulars of the utmost interest*. 
In the Bull-frog the upper labial is both notched and fenestrate, but it is never cut 
through as in the Common Frog, in which it was single at first. This corresponds with 
what is seen in the Lamprey (Muller, ‘Myxinoids,’ pi. 4. figs. 2-4, N). 
The external angles, however, are almost segmented off, showing a tendency to form 
the “ rod-shaped appendage of the labial ring ” (Muller, op. cit. pi. 4. fig. 2, Q) ; the lower 
labials are much more developed than in the common kind, and are relatively nearly as 
large as those of the Lamprey. Another myxinoid character in the Bull-frog is the large 
amount of free trabecular horns left in front of the nasal sacs after the latter are well 
formed ; they persist also in the adult as free leaf-like flaps, the divided counterparts of 
the Lamprey’s emarginate “ ethmo-vomerine plate” (Muller, op. cit. pi. 4. figs. 2-4, L). 
Full twice as many bones, “ ectosfoses ” and “ parostoses,” are found in the Bull-frog 
as compared with the common kind ; these especially abound in and on the “ suspen- 
sorium,” and have been very instructive to me in working out the Grey Frog, enabling 
me to speak more confidently of ichthyic parts and regions. 
One thing must be mentioned in : R. pipiens as in Hatteria (Huxley, “ On the 
Representatives of the Malleus and Incus,” p. 397, fig. 4), the “ suprastapedial ” retains 
its secondary fusion with the auditory sac. The cartilaginous “ annulus tympanicus ” 
w I am now drawing from unpublished material ; the dissections and drawings of the larval Bull-frogs and of 
a huge Tadpole of Pseuclis pciradoxa were made from specimens given me by Professor Flower • the adult Bull- 
frog 1 received from Dr. Murik. 
